Has anyone found a cheap source for a smoke/fog generator to diagnose vacuum leaks? I still have a pesky problem with my 1990 740GL. Thanks to Ringlee, I believe this could be my problem.

Old Bear

I use Propane to test for vacuum leaks (less messy than carb cleaner or other sprays). Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).

With the engine at a warm idle, open the valve and poke the end of the hose around each injector for a couple of seconds. If the seas leak, you should hear the engine smooth out or rev up when the propane gets sucked in and burned.

Do the same around any other suspected areas, like hidden vacuum hose ends and the intake manifold gasket area.

To block any breeze from the fan, lay a piece of cardboard from the fan shroud to the engine.
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Bruce Young,
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

This is a great tip. Propane also makes a great starting fluid. I had a lawn mower with a badly scored cylinder and because of the poor compression it would refuse to start first time in the spring. I used "propane enrichment" to get it started. I would crack open the valve and hold the torch nosel near the air cleaner and it would fire right up. I have always suspected that this would be a good trick for starting a snow blower in the cold cold winter.

Dan

Thanks Dan, that's one of the "canned responses" I've been accumulating for some of the FAQs (rather than the terse "see the FAQ", although that's sometimes appropriate, I guess.)

And thanks for the starting tip too. We both learned something, so it was a good day.

Bruce
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Bruce Young,
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

I frequently learn from your posts. I'm glad I can partially return the favor.

Dan

Thanks for the input. I'll give it a try. Next step would be to Volvo shop.

Old Bear